Trigger for high rate actuators



July 13, 1965 J, H, GAvlN 3,194,016

TRIGGER FOR HIGH RATE ACTUATORS INVENTOR Jaf/A/ 6AM/,V

fjy-f BY `Iuly 13, 1965 J. H. GAvlN TRIGGER FOR HIGH RATE ACTUATORS 2 Sheets-Sheet 2 Filed Jan. 17, 1964 1N VEN TOR.

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if ff 7% WMM United States Patent O E9e-,Elle TlilGGER FR HGH RATE ACTUA'JTGRS ohn H. Gavin, IllS Save Ave., Lancaster, Pa. `lliiled lian. 17, T1964-, Ser. No. 338,515 l2 Claims. (Cl. dil-5l) This invention relates generally to high rate pressure operated actuators and more'particularly to such actuators incorporating novel and improved self-triggering means arranged to prevent loss of the pressurizing lluid.

High energy actuators are used for a number of purposes one of the principal of which is die forming of metal parts and the like. ln such forming devices a plunger is accelerated by gas under substantial pressures to carry a die with high impact velocity against the material to be formed. ln an actuator incorporating this invention, improved triggering means are provided to hold the plunger in the cocked position which are arranged so that a substantially instantaneous release of the plunger occurs without the loss of any charging iluid.

An actuator to which this invention is particularly suited includes a cylinder or housing with a plunger slidable therein between a cocked or first position and an operated or second position. The plunger and cylinder cooperate to define a closed cavity charged with iluid under pressure. When the plunger is moved to the cocked or irst position the pressure of the fluid in the cavity increases to a relatively high-pressure. The plunger and cylinder are provided with mating surfaces which engage and seal to isolate a chamber from the main cavity when the plunger is in the cocked position and means are provided to reduce the pressure in this isolated chamber without loss of fluid to hold the plunger in its cocked position. The effective area of the isolated chamber is greater than the eiective area of the plunger within the main cavity so that a pressure induced force is created holding the plunger in its cocked position. When the plunger is to be triggered the isolated chamber is pressurized, causing the plunger to move away from the cocked position and provide complete communication between the chamber and cavity. This produces an almost instantaneous elimination of the balancing area and results in extremely high accelerations of the plunger toward the operated or the second position.

In the past actuators have been provided of this general character wherein the plunger is moved to the cocked position and the isolated chamber vented to reduce its pressure. This resulted in a loss of fluid under pressure each time the actuator was operated. In an actuator incorporating the present invention means are provided to increase the volume of the isolated chamber thereby reducing the pressure therein without loss of any of the charging gas. Therefore, it is not necessary to supply additional charging gas as the machine is operated.

lt is an important object of this invention to provide .a tluid pressure operated actuator incorporating novel and improved triggering means arranged so that the charging gas in the actuator is not lost during the operation of the triggering mechanism.

It is another important object of this invention to provide a novel and improved fluid pressure actuator having a chamber .adapted to be isolated from the main cavity of the actuator when the plunger or output member is in the cocked position in combination with means to reduce the pressure of the chamber to hold the plunger in the cocked position without loss of the fluid under pressure originally contained therein and incorporating means to automatically return the system to its initial condition.

Another important object of this invention is to provide a high rate actuator having improved triggering means and wherein the effective area of the iston is not changed during the operation.

ICC

It is still another object of this invention to provide an actuator incorporating a housing and plunger cooperating to define a variable volume cavity filled with charging fluid under pressure and cooperating when the plunger is in the cocked position to isolate a chamber from the cavity wherein means are provided to increase the volume oi the chamber to reduce the pressure thereof to retain the plunger in the cocked position without loss of any of the charging lluid.

It is still another object of this invention to provide a triggering actuator incorporating a housing and plunger provided with means to isolate a triggering chamber from the main pressurized cavity wherein an accumulator is connected by valved means to the triggering chamber to allow reduction of the pressure in the triggering chamber and thereafter return the iluid to the actuator.

lt is another important object of this invention to provide an actuator including a housing and slidable plunger cooperating to dene a main cavity and a triggering chamber isolated therefrom when the plunger is in a cocked position wherein novel and improved valved means are provided to control fluid llow between the chamber and the cavity so that the pressure in the chamber can be reduced to retain the plunger in its cocked position and thereafter increased to cause the plunger to be released.

Another object of this invention is to provide an actuator according to the preceding object wherein the valve means includes a check valve allowing fluid low only from the chamber to the cavity and a normally closed triggering valve operable to permit flow from the cavity to the chamber.

Further objects and advantages will appear from the following description and drawings wherein;

FIGURE 1 is a schematic illustration of one preferred embodiment of this invention wherein an external accumulator is provided which is adapted to be connected to the triggering chamber to increase the volume thereof and reduce the pressure therein without loss of charging gas;

FIGURE 2 is an enlarged fragmentary schematic illustration of a second embodiment wherein a single valve is provided which is operated to exhaust gas from the triggering chamber and thereafter admit gasto release the plunger;

FIGURE 3 is an enlarged fragmentary schematic illustration of a third embodiment illustrating the position of the elements when the plunger seal first engages the bore and the housing to isolate the triggering chamber from the main chamber;

FlGURE 4 is a view similar to FlGURE 3, illustrating the plunger at the top extreme position;

FIGURE 5 is a view similar to FIGURES 3 and 4, illustrating the position of the elements after the plunger has dropped down to increase the volume of theV triggering chamber thus reducing the pressure contained therein;

FlGURE 6 is a fragmentary schematic illustration of a fourth embodiment of this invention utilizing an internal accumulator including a floating piston for increasing the trigger chamber volume to decrease the pressure therein illustrating the elements at the moment the plunger seal engages the mating wall in the housing; and,

FIGURE 7 is a schematic illustration similar to FlG- URE 6 illustrating the floating piston in its retracted position in which the pressure in the trigger chamber is reduced.

Referring to the drawings, FIGURE l schematically illustrates a forming press incorporating one embodiment of this invention. The main frame it) includes a base il, a cylindrical frame member 12, :and an end cap 13. Intermediate of its ends, the frame member l2 is formed with an inwardly extending flange 1d which slidably engages a plunger or piston 16. A seal 17 on the -flange 14 engages the outer surface of the plunger 1d and prevents leakage between the plunger 16 flange' 14. seal 19 is mounted on the Ycap member 13 in engagement with the inner wall of the frame member 12 to prevent leakage therebetween. The plunger 16 in cooperation with the frame member 12 and cap 13 denes a main cavity 13 the volume of which is changed Vby]movement of the plunger 16 relative to the frame f The cap 13 is ormed with a centrally located yblind bore 21 open tothe chamber 1d and closed at its upper end by an end wall 22. A flaring entrance 23 is formed at the openend of the bore 21 Lto facilitate the entry of a head 24 formedl on the plunger 16.V The head 24 is formed with a diameter Vproportioned to closely tit the wallV of the bore 21 and is provided with a seal 26 to provide sealing engagement therebetween when ther actuators having cylinders d@ inthe base 1l symmetrically located with. respect to the plunger 16. Each actuator is provided with va piston 51 Yengageable .with the lower end face 52 of the plunger V1e. Each of the cylinders i9 is connected in parallel to va ounway valve 53 by suitable piping and is supplied with operating pressure by a pump 54. The intake ofthe pump 54 and the exhaust of 'the valve 53 are connected to a reservoir S6.

The pistons 51 are double-acting so that they may be f extended to push the Vplungerlto the cocked position and then retracted by operation of the four-way valve 53 so that they are clear of the lower end of the plunger' lle..

' Suitable dies may be mounted on the lower end face 52 chamber 28 is de ned by the head 2d and cap member y the cocked position of FEGURE l. This insures that the? desired pressure is available for operation.

VWhen the plunger reaches the upper extreme position Y suitable gases may be used;

illustrated, the chamber 23 is isolated fromthe main Y cavity 1S. The effective volume of the chamberis then increased to yreduce the pressure .therein to a pressure suioiently low to cause the plunger to be retained in the cocked position by the pressure forces. The tluid under pressure inthe cavity 1S then `produces a force on the' plunger 16 which is equal 'tod the pressure times'the dif-" ference in the ellective area of the head 24 and the shanky Y onthe plunger lo which overcomes the weight ofthe plunger and retains it in the upward position so long as the pressure in the chamber 2S isV maintained ybelow the pressure in the cavity 18 by an amount suicient to of the plunger 16 and the'upper end face l5"? of the base lll. YThese dies have not been illustrated since they form no part of this invention.v Normally, however, they are arranged so that downward movement ofthe plunger 16 causes thek dies'to work or form the desired article when the plunger Vcauses the upper die to impact the material at a high rate of velocity.l Suitable shock absorbing de-V vices 53 are provided to support the entire system.

The valve 4 6 may be manual or automatic to supply any .required Vmake-up gasl from the reservoir Vifi .tothe cavity .13 when the plunger l16 is in its operated position since the pressure in the cavity is lowest in this position.

Nitrogen is often used as a charging gas, however, other In this way the charge in :the chamber 13 is maintained at the desired minimum value. It should be @realized that when the impact energy is Vto be changed, the pressure of precharge should be raised or loweredfor such .an adjustment. The valve 46, if automatic, should be such thatA backilow is prevented as the plunger 16 is raised, increasing the pressure in the cavity 18.` n

in operation, with the valve 31 closed 'and the. triggering valve 32 open, the con'trol'valve 53 'is operated to extend the pistons 51' and raise the plunger 1e against the pressure in the cavity lluntil the plunger reaches the uppermost .position as illustrated. At the moment the seal .'26 engages the lower end of the .bore '21 the ,pressure .in the y Vchamber 28 is equal to the pressure in the cavity `18 so the seal 26 can smoothly vmove into engagement -with'the produce aY pressure unbalance great enough to overcome to differential pressures thereacross. The piston 37 operates to divide the laccumulator into an upper gas-receiving chamber 3% and a lower liquid-receivingv chamber 39.

A pump 41 is Vprovided to pressurize Vthe liquid chambery 39. The intake of the pump is connected to a reservoirV 42 and the output is connected to a valve 43 which can be selectively Yoperated to supply liquid underpressure frornthe pump 4:1 to the chamber 39, or exhaust the chamber 39 to the reservoir 42.

The triggering valve 32 is connected through appreswall of the ibor-e without damage. APreferably this occurs before the plunger reachesV its uppermost position.

Continued upward movement after the seal 26 engages the bo-re 21 .decreases the volume ofthe chamber'ZS and causes vgas to ilow through the triggering valvemaintaining the pressure in the chamber 2S and cavity 18 equal. Once theplunger reaches the fully cocked or upward position illustrated, the triggering .valve 32, is closed and the accumulatorvalve 31 is opened.' During this time the .valve t3 vis openated to permit: exhaust fromV the chamber 39 Ito vthe reservoir 42, and the .pumpY d1 is either byV-passedor shut ott. lSince the pressure in the chamber 39 1s. maintained at substantiallyatmospheric pressure, the piston 3T Will move down under the influence of the Vpressure inthe chamber 2S as .soon as the accumulator valve 31 is opened.v This increases the effective volume of the chamber 28 and reduces the pressure therein. The capacity of the accumulator 3d must be suiiiciently great 'to produce a reduction in pressure in the chamber '23 so that the-Huid orces on the Vplunger 16 will produce suiiicient yupward force to overcome lthe weight of the plunger. At thisV time `the plunger ,15 is retained in its upper positionl by t-he Afluid pressurel forces and the valve 53 1s. operated to retract the pistons 51. The valve 31 is then closedto prevent overpressurization of the accumsureline 44 to the main cavity 13 and also'through a line 45 to a charging valve d5. The charging valve lo maintained under pressure by a motor-driven pump eti.

A pair of 1hydraulic jacks are provided to liftthe plunger 16 to its cocked position illustrated in FGURE V'ulator 34 when the triggering valve is opened to actuate the plunger 16. When itis desired to operate the press the triggering valve 32 is opened to'permit ilow'fr-om the cavity 18 into Ithe chamber' .lffth'ere-by increasing the pressure in the chamber 28. This removes the balancing luid forces and causes'downward movement of the plunger carrying the seal 26 out'of engagement Vwith the Wall of the bore 21 so that the chamber'ZtS isV no longer isolated 5 from the main cavity lli. Therefore, the gas under pressure in the main cavity i8 acts on an elective area equal to the area within the seal 17 to produce a high accelerating force :on the plunger which carries it down to its operated position. Since high pressure in the chamber llt; a-cts on a relatively large etlective area, the plunger very rapidly accelerates to produce a very high impact energy.

After the plunger reaches the lower most position, the valve 43 is operated to connect the output of the pump 4l to the accumulator chamber 39 and the valve 3l is opened to connect the chamber 3S to the cavity i8. The pump operates to supply suicient pressure to move the piston 37 up to its initial position, thus returning any charging gas to the system. As 4soon as the piston 37 reaches its upper position, the valve 31 is closed and the system is back in its initial `condition with all of the charging gas returned to the cavity 18. Therefore, no charging gas is lost during the operation of the system. Make-up gas therefore must only be provided to replace leakage which is very small. This invention thus eliminates any loss of charging gas yduring normal cycling of the system and operating costs of the mechanism are reduced.

In FTGURE 2 a second embodiment of this invention is illustrated which eliminates the need of a separate accumulator. ln this .ligure only the triggering portion of the system is illustrated. lt should be understood, however, that the frame l@ and actuators for pushing the plunge-r up to t e cocked position would be identical with the embodiment of FIGURE l. Corresponding reference materials are utilized in the second embodiment to indicate similar parts to the embodiment of FGURE l, but an cr is :added .to indicate the fact that the reference is tothe second embodiment of FGURE 2.

The cap member 13a in this embodiment is again formed with a blind bore Ela; however, the depth of the bore is deeper than in the irst embodiment. Here again, a flaring entrance 23a is provided to facilitate the entrance of the head 24a of the plunger loa. rvThe seal 26a engages the wall of the bore 2in when the plunger lea is a substantial distance from the upper extreme of its travel, thus isolating the chamber 28a from the main cavity lh at a point in the stroke of plunger Well before the uppermost extreme position. The triggering valve 32a provides a uid connection between the lcharnber 23a and the cavity ld when it is open and isolates the two when it is closed. The triggering valve is also connected through a branch line fida to the charging valve (not illustrated) in the same manner vas in the first embodiment.

The operation of this embodiment is as follows: the jacking actuators are operated to raise the plunger la with the triggering valve 31a open. At the point of the stroke, illustrate-d in FGURE 2, when the .seal 26a first enga-ges t-he wall of the bore Zia a lluid connection is provided between the `chamber 23a and cavity 1&2 through the open valve 32a. Therefore, continued upward movement of the plunger, until its upper end engages the end wall 22a, operates to pump charging gas out of the chamber 2da into the ycavity ida. W en the plunger is in this 'topmost position, the volume of chamber' is lat a minimum and the triggering valve 32a is closed. The jacking actuators are then retracted. This causes the plunger la to move ldownward increasing the volume of the chamber 2S@ until the pressure therein drops and the plunger ida is pressure-suspended in a manner similar to the nrst embodiment.

The length of the bore Zla must be suliiciently long to permit the increase or" the volume of the chamber 28a during this phase of operation a suliicient degree to reduce the pressure therein to a value which will produce pressure suspension or support of the plunger. When the jacking actuators are fully retracted, the triggering valve 32a can be opened to allow pressure to iiow from -the .cavity iba into the chamber Zlio thus triggering the plunger loa and initiating its downward movement. Here again, as soon as the seal 26a moves out of the bore Zla, the full pressure in the cavity 13a acts on the plunger to produce a very high rate of acceleration toward its extended position. With this embodiment the requirement of a sepa-rate accumulator is eliminated while still :retaining the desirable feature of eliminating all triggering losses of the charging gas.

In the embodiment or FIGURES 3 through 5, reference numerals referring to similar elements will be used with a o to indicate that the third embodiment is indicated. Hereagain, only the cap member 3,3 and the cooperating triggering and suspending structure is illustrated with the understanding that the remaining frame and jacking actuators will be the same as in the lirst embodiment. In this embodiment a check valve iib is provided to connect the chamber Zlib with the main cavity lb. This check valve is arranged to permit llow in one direction only from the chamber Zdb to the cavity lh, and to prevent ow in the opposite direction. Hereagain, a triggering valve 32k is provided and the length of the bore 2lb is arranged so that the plunger le?) can move downward from its eX- treme upper position to decrease the pressureI in the charnber 28]) so that the plunger can be duid-supported in its coclred position.

ln operation, upward movement of the plunger lob carries the seal 25,5 into engagement with the wall of the bore 2lb when the position of FlGURE 3 is reached. During this movement the valve 3215 remains closed. As the plunger is moved upward between the position of FlGURE 3 and the position of FIGURE 4, reducing the volume of the chambe' 23h to a minimum, the charging gas flows out of the chamber 23h through the check valve 531') into the main chamber lb. Then, as the jacking actuators are retracted, the plunger lob moves downward to the position of HEURE 5 increasing the volume of the chamber Zdb and causinff the pressure therein to be greatly reduced. The checlr valve Elib prevents reverse ow and the triggering valve 32h is closed at this portion of the cycle. T he plunger therefore remains in the position of FTGURE 5 until the triggering valve 32h is opened to admit charging gas into the chamber 28]; and thus initiate downward movement of the plunge-r. This embodiment utilizing the check valve o'sb again eliminates the necessity of a separate accumulator, but also eliminates the necessity of operating the triggering valve twice during the cycle. When the actuator is to be operated, the triggering valve 32h is opened to pressurize the chamber Zlib and the plunger T16!) moves to the extended position.

ln the fourth embodiment of FIGURES 6 and 7, a c is added to reference numerals to indicate that reference is being made to the fourth embodiment. Hereagain, the complete machine would utilize a frame assembly lll and jacking actuators in a manner similar to the irst embodiment of FEGURE l. ln this embodiment a lioating piston 59e is mounted in the cap )13C above the bore Zic. The cap is preferably formed with an enlarged bore @le joined to the bore Zllc by a radial shoulder 62e which serves as a stop to limit the downward movement or the lioating piston 5de. A seal 63C on the floating piston 59C engages the wall of the bore 61C. A chamber efec is therefore provided above the lloating piston 59e and is connected through a port 66C to a valve 43C which is operable to selectively connect the chamber 64C to the pump die, the reservoir 42C, or isolate the chamber elle from both the pump and the reservoir. Hereagain, the triggering valve 32C is operable to isolate the chamber Se from the main cavity 18C or to provide free communication therebetween.

In this embodiment the chamber 28C is dened by the lower side `oli the oating piston 59C and the wall of the bore Zic in cooperation with the head of they plunger loc. The, valve 43e is operated to connect the chamber 64o to the pump die while the plunger is in its extended position and the minimum pressure is in the main cavity 18C.

g This pressuriz'es the chamber 6ft-c and pushes vthe floating piston 59e to its. position against the shoulder 62C aga-inst the precharge pressure. The valve 43e is then closed .to

isolate the chamber 64e from both the pump and reser- Voir. Since liquid fills the chamber 64C, and liquid is substantiaily incompressible, the floating piston remains inV eris retained in this position and the valve 43g is operated t to the position in which it connects the chamber 64eV to the reservoir 42e thus 'exhaustingV the chamber V6de and allowing the floating piston to raise upto the position of FIGURE' 7. This increases the volume of the chamber 28e and causes the pressure therein to be reduced. Normally the plunger ier: will raise slightly during the moVement'ofthe-oating piston 59e until an equilibrium condition is reached wherein the pressure 'forces balance the weight of the plunger. This equilibrium condition mayrequire someI positive pressure in the chamber '28C depending opon the relative areas of the seals 26'and 17, the weight 0f the plunger and the pressure inthe main cavity 18e. Y A

When it is desired to trigger the plunger and initiate its downward movement, the triggering valve 32C' is opened to provide communication betweenthe chamber 23C and the main cavity litio thus increasing the pressure in the chamber 2SC and initiating the downward movement Vof the plunger. After the plunger reaches its extended position, the valve 43e is again operated to connect the chamber 64C to the pump 41C and cause the iioating piston 59C to move down to the posi-tion in engagement with the should-er 62e. This returns the system to its initial condition and again prevents any loss of charging fluid.

In all of these embodiments the' chamber defined by the head ofthe plunger and the cap member is arranged so that the lpressure can be reduced therein Without loss of charging gas from the system. In each case the effecseal between said plunger and housing having a rst eiective area,-opposed walls on said housing and plunger proportioned to mate when said plunger is in said first position, second seal means cooperating 'with said mating walls to define at least a portion of a chamber isolated i from said cavity when-said plunger is in said tirst position, said second seal means having a second efective area `greater than said iirst eiective area, valved means connected Abetween said chamber and cavity selectively op- Yerable Yto isolate saidchamber and cavity and to provide communication therebetween, compressible iluid under pressure in said cavity, and means toV increase the volume of'said chamber when Ysaid valved means are closed reducing the pressure thereof without releasing the fluid contained therein, the pressure in said chamber being Y reduced to a pressure suiciently low to produce a force -When said plunger is in saidiirst position, valved'means connected between said chamber and cavity selectively operableto isolate said chamber and cavity and to provide lcommunication therebetween, iiuid under pressure in said cavity, and an accumulator connected to said chamber operable to expand the fluid therein and reduce the pressure thereof without releasing the fluid, and pump means connected to said accumulator and operable to return duid from said accumulator 'to said cavity.

V4. An actuator comprising a housing, a plunger slidable in said housing between rst and second positions cooperating to define a cavity the volume of which is retive volum-e of .the chamber 23 is increased to reduce the Y without departing from the scopeY of the invention as deiined in the following claims. Y I claim: Y L An actuator able in said housing between iirst and second positions cooperatingtodene a cavity the volume of which is reduced by movement of said plunger to saidV vrst position, opposed walls on said housing and plunger prioportioned to mate when saidplunger is in said'iirst position, seal means cooperating with said mating walls to deine atleast a portion of a chamber isolated from said g cavity when `said plunger is in said iirst position, valved means connected between said-chamber and'cavity se-V lectively operable Vto isolate said chamber and cavity and provide communication therebetween, ycompressible fluid underpressure` in said cavity, and means operable toincreasethe volume'of said chamber when said valved,

comprising a housing, a plunger slidduced by movement of said plunger to said iirst position,A opposed walls on said housing and plunger proportioned to mate when said plunger is in said first position,` seal means cooperating with said mating walls to denne at least a portion of a chamber isolated from t said cavity when Vsaid plunger is in said iirst position,

valved means connected between said chamber and cavity selectively operableto isolatesaid Vchamber. and cavity V and to providercommunication therebetween, uid under means areclosed reducing the pressure thereofwithout releasing the iiuird contained therein thereby producing Vpressure balancing of said plunger.

2. An actuator comprising a housing, a plunger slidable in said housing between iirst( and second positions cooperating to'define a cavity the volume of which is reduced byV movement fof `said plunger Vto said Atirst position, a iirst p pressure in sai-d cavity, and an accumulator including a Vpressure responsive member connected to said chamber movable under the influence of iiuid pressure therein froman initial position to' expand vsuch fluid and reduce the pressure thereof without releasing such fluid, and means connected to move said pressure responsive 4member backto its initial position and return fluid to said cavity. Y

i 5'. An actuator comprising a housing, a plunger slidable in` said housing betweenwirst and second positions cooperating to define a cavity the volume of which is 'reduced by movement of said plunger to said -iirst position,

Vopposedy walls on said housing and plunger proportioned accumulator intoa gas section and a liquid section, said pressure responsive element Vbeing movable from an initial positionunder the influence-of gaspressure in said chamber to increase the Volume of such gas and reduce its pressure, and pump means connected-to, said accumulator V'and-operable to supply liquid under pressureto saidy liquid section and return said pressure responsive element to said initial position.

o. An actuator comprising a housing, a plunger slida'ole in said housing between first and second positions cooperating to define a cavity the volume of which is reduced by movement of said plunger to said first position, opposed walls on said housing and plunger proportioned to mate when said plunger is in said first position, seal means cooperating with said mating walls to define at least a portion of a chamber isolated from said cavity when said plunger is in said first position, valved means connected between said chamber and cavity selectively operable to isolate said chamber and cavity and to provide communication therebetween, fluid under pressure in said cavity, and an accumulator in said frame aligned with said chamber, a pressure responsive element in said accumulator open on one side to said chamber, said pressure responsive element being movable from an initial position under the influence of pressure in said chamber to increase its volume and decrease its pressure, and pump means connected to the other side of said pressure responsive element to move such element back to its initial position.

7. An actuator comprising a housing, a plunger slidable in said housing between first and second positions cooperating to define a lcavity the volume of which is reduced by movement of said plunger to said first position, a bore in said housing, a head on said plunger positioned in said bore when said plunger is in said first position, seal means between said bore and head cooperating therewith to define at least a portion of a chamber isolated from said cavity when said plunger is in said Irst position, fluid under pressure in said cavity, a triggering valve operable to supply fluid under pressure to said chamber, and means operable to increase the volume of said chamber reducing the pressure thereof without releasing the fluid contained therein.

`S. An actuator comprising a pair of telescoping members movable relative to each other between first and second positions and cooperating to dene a fluid tight cavity the volume of which is reduced by movement of said members to said first position, a compressible fluid under pressure in s-aid cavity normally urging said members toward said second position, said members cooperating to define 4at least a portion of a fluid tight chamber isolated from said cavity when said members are in sai-d first position, means operable to incre-ase the volume of said chamber without loss of fluid therein while said chamber is isolated from said cavity to reduce the pressure therein, said members being proportioned so that said members are retained substantially in said first position by fluid under pressure when the pressure in said chamber is reduced, and valved means operable to connect said cavity and chamber to increase the press-ure in said chamber and cause pressure induced movement of said members to said second position.

9. An actuator comprising a cylinder, a plunger movable in said cylinder between .first and second positions, said cylinder .and plunger cooperating to define a cavity the volume of which lis Ireduced by movement of said plunger to said first position, a compressible fluid under pressure in said cavity, said cylinder being formed with a blind bore, a head on said plunger positione-d in said bore when said plunger is adjacent to sa-id first position `and operating to isolate a chamber defined by said bore and head from said cavity, -v-alved means operable to permit flow of fluid from said chamber to said cavity as said head moves along said bore when Jsaid plunger moves to said first posit-ion, means operable to reduce the pressure in said chamber, said plunger and cylinder being proportioned so that said plunger is retained substantially in said first position by said fluid under pressure in said cavity when the pressure in said chamber is reduced, said valved means being operable t-o connect said cavity and chamber yand increase the pressure in said chamber causing pressure induced movement of said plunger toward said second position.

di?. An actuator comprising a cylinder, a plunger movable in said cylinder between first land second positions, said cylinder ,and plunger cooperating to define a cavity the Volume of which is reduced by movement of said plunger to said first position, a compressible fluid under pressure in said cavity, sai-d cylinder being formed with a blind bore, a head on said plunger positioned in said bore when said plunger is adjacent to said first position tand operating to isolate 'a chamber defined by said bore and head from said cavity, valved means openable to permit flow of fluid from said chamber to said cavity as said head moves along said bore when said plunger moves to said first position, movement of said plunger from said first position toward said second position increasing the volume of said chamber .and decreasing the pressure therein, said plunger and cylinder being proportioned so that said plunger is retained by pressure in said cavity substantially in said first position when the pressure in said chamber is decreased by movement of said plunger away from said first position, said valved means being operable to connect said cavity and chamber and increase the pressure in said chamber causing pressure induced movement of said plunger toward said second position.

11. An actuator comprising a cylinder, `a. plunger movable in said cylinder between first and second positions, said cylinder and plunger cooperating to define a cavity the volume of which is reduced by movement of said plunger to said first position, 'a compressible fluid under pressure in said cavity, said cylinder being formed with ya blind bore, a head on said plunger positioned in said bore when said plunger .is .adjacent to said first position and operating to isolate a chamber defined by said bore and head from said cavity, a first valve operable to permit flow of fluid only from said chamber to said cavity, movement of said plunger from said first position toward said second position increasing the volume of said chamber tand decreasing the pressure therein, said plunger and cylinder being proportioned so that said plunger is retained substantially in said first position by said fluid under pressure in said cavity when the pressure lin said chamber is decreased by movement of said plunger away from said first position, land a second v-alve operable to connect said cavity and chamber and increase the pressure in said chamber causing pressure induced movement lof said plunger toward said second position.

12. An actuator comprising a cylinder, a plunger movable in said cylinder between first and second positions, 'said cylinder and plunger cooperating to define a cavity the volume of which is reduced by movement of said plunger to said first position, a compressible fluid under pressure in said cavity, said cylinder being formed with a blind bore, a head on said plunger positioned in said bore when said plunger is :adjacent to said first position and operating to isolate a chamber defined by said bore and head from said cav-ity, a check valve connected to permit flow of fluid only from said chamber to said cavity as said head moves along said bore when said plunger moves to said first position, movement of said plunger from said first position toward said second posi- .t-ion increasing the volume of said chamber and decreasing the pressure therein, said plunger and cylinder being proportioned So that said plunger is retained substantially 4in said first position by said fluid under pressure in said cavity `when the pressure in sai-d chamber is decreased by movement of said plunger away from said first position, and a triggering valve operable to connect said cavity and chamber yand increase the pressure in said chamber causing pressure induced movement of said plunger toward said second position.

(References on following page) References Cited bythe Examiner UNITED STATES PATENTS BetyKet a1. 200-82 Murek 91-29 12 ,Y Ottestad 91-165 Murek 91-29 Ottest'ad et Ial 91--25 Ottestad et a1. 113-45 Murek 91--25 Brown 91-25 Brown 91-25 JULIUS E, WEsLPrimary Examiner. 

1. AN ACTUATOR COMPRISING A HOUSING, A PLUNGER SLIDABLE IN SAID HOUSING BETWEEN FIRST AND SECOND POSITIONS COOPERATING TO DEFINE A CAVITY THE VOLUME OF WHICH IS REDUCED BY MOVEMENT OF SAID PLUNGER TO SEE FIRST POSITION, OPPOSED WALLS ON SAID HOUSING AND PLUNGER PROPORTIONED TO MATE WHEN SAID PLUNGER IS IN SAID FIRST POSITION, SEAL MEANS COOPERATING WITH SAID MATING WALLS TO DEFINE AT, LEAST A PORTION OF A CHAMBER ISOLATED FROM SAID CAVITY WHEN SAID PLUNGER IS IN SAID POSITION, VALVED MEANS CONNECTED BETWEEN SAID CHAMBER AND CAVITY SELECTIVELY OPERABLE TO ISOLATE SAID CHAMBER AND CAVITY AND PROVIDE COMMUNICATION THEREBETWEEN, COMPRESSIBLE FLUID UNDER PRESSURE IN SAID CAVITY, AND MEANS OPERABLE TO INCREASE THE VOLUME OF SAID CHAMBER WHEN SAID VALVED MEANS ARE CLOSED REDUCING THE PRESSURE THEREOF WITHOUT RELEASING THE FLUID CONTAINED THEREIN THEREBY PRODUCING PRESSURE BALANCING OF SAID PLUNGER. 